Optimize InternalUsageDiagnosticAnalyzer: replace ToDisplayString with symbol equality

[Copilot]

HasInternalAttribute was calling ToDisplayString() on every attribute class for every analyzed symbol to match against EntityFrameworkInternalAttribute by name — allocating a new string each time. This was measured at ~36% of inclusive time in a perf trace, contributing ~2 MB of extra string allocations per build.

Changes

• Cache attribute symbol at compilation start: Register actions via RegisterCompilationStartAction and resolve the INamedTypeSymbol for EntityFrameworkInternalAttribute once per compilation using GetTypeByMetadataName.
• Replace string comparison with symbol equality: HasInternalAttribute now uses SymbolEqualityComparer.Default.Equals(a.AttributeClass, internalAttributeSymbol) — no allocation.
• Thread cached symbol through call chain: All private methods that previously called HasInternalAttribute() now accept and forward INamedTypeSymbol? internalAttributeSymbol. If EFCore isn't referenced (null), the attribute check is skipped entirely.

// Before: allocates a string on every attribute of every symbol
private static bool HasInternalAttribute(ISymbol symbol)
    => symbol.GetAttributes().Any(a =>
        a.AttributeClass!.ToDisplayString()
        == "Microsoft.EntityFrameworkCore.Infrastructure.EntityFrameworkInternalAttribute");

// After: resolved once per compilation, compared by reference
private static bool HasInternalAttribute(ISymbol symbol, INamedTypeSymbol? internalAttributeSymbol)
    => internalAttributeSymbol is not null
        && symbol.GetAttributes().Any(a =>
            SymbolEqualityComparer.Default.Equals(a.AttributeClass, internalAttributeSymbol));

• Fixes InternalUsageDiagnosticAnalyzer uses non-optimal ToDisplayString check to find matching attribute #38723

[Copilot]

Pull request overview

This PR optimizes InternalUsageDiagnosticAnalyzer by removing repeated ToDisplayString() allocations during attribute checks and replacing them with cached symbol equality comparisons, addressing perf findings from #38723.

Changes:

• Resolves EntityFrameworkInternalAttribute once per compilation via RegisterCompilationStartAction + GetTypeByMetadataName.
• Replaces per-attribute string formatting/comparison with SymbolEqualityComparer.Default.Equals(...) against the cached symbol.
• Threads the cached INamedTypeSymbol? through the analyzer’s private call chain so the attribute check becomes a fast no-op when the symbol can’t be resolved.